360 THE POPULAR SCIENCE MONTHLY 



Physiology 



In this article, so far, we have dealt with the natural-history side of 

 hibernation, explained what is meant by the various terms used in con- 

 nection with this state and in what respect the condition itself differs 

 in the various animals subject to its peculiar manifestations : a condi- 

 tion provided by nature to tide an animal over a period when its very 

 existence, owing to scarcity of food, becomes too difficult or even impos- 

 sible to maintain; so by preserving the animal's life allows it to per- 

 petuate its species. 



We will now pass on to consider the purely physiological phases and 

 phenomena of this state. 



In hibernation all the activities of the body are greatly reduced, the 

 temperature of the animal is lowered and even falls to a point slightly 

 above that of the surrounding media. As it has been pointed out above, 

 animals which hibernate do not belong to any one class, but examples 

 are met with in mammals, reptiles ( ?), amphibians, insects, molluscae, 

 but curiously enough, no case is known among birds. 



In some cases, previous to entering the hibernating state, the animal 

 stores up food in its den or nest, on which it feeds when it wakes at 

 intervals during its winter sleep. This is hardly pure hibernation, as 

 in the true cases there is a special accumulation of fat in the animal's 

 body before the commencement of the torpid state (the animal not 

 waking to feed) and this serves as food during the hibernating period. 

 A peculiar physiological change is here involved — a herbivorous animal 

 becomes carnivorous, this being caused by the animal living on its own 

 flesh, hence the excretions (small) of the animal become profoundly and 

 completely altered in their chemical characters. 



A low temperature is the cause generally assigned for the production 

 of hibernation, but a more careful consideration of the facts long ago 

 showed that cold could not be the sole cause of the phenomenon. Most 

 observers who have worked on the subject have found that extreme cold 

 will not cause an active animal to hibernate; although Saissy has ob- 

 served that continued cold, and a limited amount of air for respiration 

 caused a marmot to pass into a typical hibernating condition, even in 

 summer. Against this we have Vernon Bailey's experiments with 

 spermophiles (first cousins of the marmots or ground-hogs), which 

 showed that in the case of hibernating animals a few degrees lower 

 temperature changed the torpid state into one of death. 



Mangili found that torpid marmots and bats were awakened by 

 exposure to severe cold and that lessened or confined air would not cause 

 hibernation. Dormice have been kept in a warm room throughout the 

 winter and yet they hibernated and were not aroused when the extreme 

 temperature was 20° C. The warmth, however, delayed the onset of 

 torpidity by two months and made it less profound. Again, as has been 

 mentioned before, hibernation may take place in the dry hot season. 



